The invention relates to antistatic vacuum cleaning devices and/or to blowers that move air through a long flexible hose.
There are numerous circumstances in industrial manufacturing operations wherein it is highly desirable to be able to provide a high degree of cleaniness of a work area, workpieces, or equipment. This is often done by means of a suitable industrial vacuum cleaner. Typically, the vacuum cleaner (or blower) utilizes a long piece of flexible hose connected at one end to a vacuum producing mechanism and having a pickup nozzle or the like at the other end, with a control valve on the nozzle for turning on or off the suction at the pickup nozzle. Those skilled in the art know that a quantity of air moving at high speed through an electrically insulative hose or tube often produces buildup of electrostatic charge in the vacuum tube or hose, and that if the vacuum pickup nozzle is brought sufficiently close to a conductive object, such as a grounded conductive workpiece, a piece of test equipment, or the like, an electrostatic discharge will occur. An electrostatic discharge produces a very large surge of current for a very short period of time. It is well-known that such electrostatic discharges can cause many kinds of serious problems, including destroying electronic equipment, producing data errors in electronic data processing systems, etc. Therefore, there has been a continuing need to avoid the effects of electrostatic discharges from industrial vacuum cleaners used to clean such equipment and work areas. Various techniques have been utilized to avoid static charge buildups, including using braided stainless steel wire shields on the vacuum hoses. However, there are various problems that make use of braided stainless steel grounding shields unsatisfactory for industrial vacuum cleaners. For example, an electrical ground connection between equipment being vacuumed and the vacuum producing mechanism could result in an electrical short circuit if the vacuum nozzle inadvertently touched a high voltage conductor in the area being cleaned if the flexible hose is covered with the braided stainless steel electrically grounded shield. Braided stainless steel shields often make the hose too stiff to be conveniently used for some vacuum cleaning operations. U.S. Pat. Nos. 1,223,864, 2,047,216, 2,263,221 and 3,070,132 disclose use of conductors embedded in and/or traversing the length of tubular vacuum hoses to prevent electrostatic charge buildup. However, in each of the disclosed devices, the embedded conductors in the flexible tubing are electrically connected at each end of the hose or tubing to electrically grounded conductors. U.S. Pat. Nos. 3,382,524 and 3,387,319 disclose vacuum cleaners with embedded helical coils in the vacuum hoses for conducting electrical signals from control switches on the handle of the vacuum attachment to a motor contained in the main canister unit. U.S. Pat. Nos. 1,901,330, 1,600,549, 3,555,170 and 3,819,069 disclose use of helical coil springs in flexible tubing to provide additional strength, but do not deal with the problem of electrostatic charge buildup in the hoses. Thus, the state-of-the-art seems to be that all prior art describing any electrical function for embedded helical wires in a vacuum hose requires that the embedded conductors be connected at one end to a grounded conductor that conducts electrical charge away from the helical conductor in the tubing, either to discharge electrostatic charge buildup or to conduct a control signal to a receiving unit.
Thus, there remains an unmet need for a technique for avoiding electrostatic discharges from a flexible vacuum cleaner hose or tube being used to clean areas and/or equipment and/or components that would be damaged by electrostatic discharge, yet providing the safety of having the vacuum pickup nozzle completely electrically isolated from the vacuum-producing mechanism.